MacPorts is a package manager that simplifies software installation on OS X. I've put together a Portfile to build NEURON with Python and parallelization support. After installation of MacPorts, NEURON can be installed with an installation script that downloads the Portfiles and adds them to the MacPorts index:

[UPDATE 2015-08-12] Updated to NEURON 7.4 / IV 19
[UPDATE 2015-09-30] Portfiles are now on github
[UPDATE 2015-10-01] There's a MacPorts ticket to get this integrated into the main repository
[UPDATE 2015-12-02] Added support for Python 3.5
[UPDATE 2015-12-02] Updated to NEURON 7.4 rel-1370
[UPDATE 2019-08-23] Fixed some bugs to make things work with the latest versions of Mac OS and MacPorts